Jon asked the Naked Scientists: Hi there, could u please help with a science question. Is it possible to produce a "vanishing spray", as used in soccer games, that does not foam up and is more like a spray paint that vanishes. Thanks.What do you think?

A spray paint that was highly visible would need a lot of liquid, containing some filler which is highly visible. Paints typically use fillers like titanium dioxide (lead oxide having been banned due to toxicity).

But to get this highly visible filler to become transparent is quite a challenge! And it must not kill the grass, or leave a slippery patch on the grass (that could cause a later accident).

I think the foaminess is the secret to being highly visible when first sprayed, and yet disappearing into a damp spot on the grass in a minute or so. The foam contains very little liquid - it is mostly gas, which dissipates into the atmosphere as the bubbles collapse.

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